Power management in modem computer systems plays an important role in conserving energy, managing heat dissipation, and improving system performance. For example, modem computer systems are often designed for use in settings where a reliable external power supply is not available, making power management important for energy conservation. Even when reliable external power supplies are available, power management within the computing system can reduce heat produced by the system enabling improved performance of the system. Computing systems generally have better performance at lower ambient temperatures because key components can run at higher speeds without damaging their circuitry.
One approach to power management involves the implementation of various power states in system devices, where placing a device into a relatively low power state reduces energy consumption. The tradeoff to operating a device in a low power state is typically a reduction in the level of performance of the device. It should be noted, however, that the operation of some devices might in fact be dependent upon on the operation of other devices. For example, a processor might have a cache that is snooped by other processors, where placing the processor in a lower power state could negatively affect snoop latencies experienced by the other processors. Simply put, a power state transition in one device may prevent other devices from functioning at a desired level of performance.